Tag Archives: ACA

It takes patience to be a scientist. Research can be time consuming, especially when you’re working in the Forest Products Laboratory’s (FPL) Durability and Wood Protection research work unit. Part of the unit’s mission is to treat wood with preservatives and track how long the treated wood can fend off decay. Success can mean decades-long studies.

FPL’s Valley View field test site.

Recently, several members of the unit made the trek to FPL’s Valley View test site, an unassuming field west of Madison, Wisconsin, where wood in various forms is left to endure the elements, often for years. Their mission: to inspect treated wood stakes that have been buried in the ground for 40 years.

Ground-level view of intact 2 x 4 field stake showing no visible deterioration after more than 40 years of soil contact.

The stakes, both solid wood and plywood, are made of southern pine or western wood species, such as Engelmann spruce and Douglas fir. They were treated with either chromated copper arsenate (CCA) or ammoniacal copper arsenate (ACA).

The results are astounding. There were stakes, both solid wood and plywood, that achieved a rating of 10 (sound) after 40 years of soil contact. For comparison, untreated southern pine stakes in contact with soil typically last one-and-a-half to two years before failure (rating of zero) due to decay fungi.

Field tests are critical for establishing the durability of treated wood products that are used for construction of decks, bridges, and utility poles. The test site at Valley View has been maintained by FPL since the early 1950’s. Matched sets of many of the studies at Valley View site are also installed in the Harrison Experimental Forest in southern Mississippi, which represents a more severe decay environment due to increased average temperature and rainfall.

Examples of sound (rating of 10) 2 x 4 (top) and plywood field stakes after 40 years of soil contact in southern Wisconsin.